There are reports that one of the causes of age-related cataract is an autoimmune reaction to the lens. The autoantibodies reported to cause this response do not appear to be present in the samples that we have examined. We have found that there is one protein that is immunoreactive in all the sera tested. This protein was mapped by two-dimensional gel electrophoresis, and the spot maps to the area of the gel generally occupied by the gamma-crystallins. This protein was cut out from the gel and is currently being sequenced.